INTRODUCING A NEW ESTIMATION METHOD FOR CALCULATING THE EFFECT OF NATURAL VENTILATION CONTROL IN HIGH RISE BUILDINGS WITH BUOYANCY DRIVEN VENTILATION

Study on the performance evaluation of natural ventilation control in office buildings (Part 2)

Abstract

 As natural ventilation significantly contributes to energy savings and enhances comfort, it has been adopted in many buildings. However, to maintain a comfortable room environment, including the lower limit control for room temperature, it is necessary to control the natural ventilation rate by adjusting the opening area or opening time (referred to as opening ratio). Thus, we proposed a new airflow balance simulation tool, based on Proportional-Integral-Derivative (referred to as PID) control theory, to evaluate the performance of natural ventilation control in office buildings. The proposed tool can approximately solve the thermal and airflow balance by simply adding to the existing thermal load calculations. We focused on buoyancy driven ventilation, and analyzed the following parameters using the proposed simulation tool: change in neutral pressure level, thermal load reduction, and room environment.

 First, when natural ventilation rate is adjusted by PID control, controllability varies depending on the values of proportional gain, integral gain, derivative gain (K_p, K_i, and K_d) and calculation time interval. Therefore, parametric analysis was considered the most appropriate technique for evaluation.

 Next, following the study of the calculation method in Chapter 4, the authors confirmed the fundamental effect of natural ventilation control using the proposed simulation tool. A ten-story buildings was used to analyses the performance of the proposed method. 1) The authors calculated characteristics values for specific representative week and months in the year. Under Tokyo weather conditions, opening ratio was operated from April to May and from October to November. There was no significant difference in the amount of heat extraction between “Controlled” and “Uncontrolled”natural ventilation. On the other hand, when lower limit for room temperature control was introduced, the number of hours at temperatures of 24 °C or less had decreased by 18.2 h. 2) The authors also calculated air changes per hour and natural ventilation hours due to the introduction lower limit for room temperature control. When lower limit for room temperature was introduced, the opening ratio of the lower floor had decreased. Subsequently, because of neutral pressure level raised, the number of natural ventilation hours on the nine-story or higher had increased. 3) The authors calculated room air temperature, natural ventilation hours and equipment load due to the alternative lower limit for outdoor temperature when natural ventilation was introduced. When the lower limit for outdoor temperature was 15 °C, the heat extraction increased by approximately 1.8 times and the equipment load was reduced by 2.1 % compared to the lower limit outdoor air temperature, which was 18 °C.

 In this paper, the chimney air temperature is calculated as the average value of the interior zones of each floor. In the next paper, the authors will propose a new calculation method to solve the chimney air temperature and improve the accuracy of the performance evaluation of office buildings with natural ventilation control.